As one skilled in the gas turbine engine technology appreciates the performance of the gas turbine engine for powering aircraft is ever increasing and as a consequence to this high performance, the pressure drop across a single stage high pressure turbine is sharply increasing. This large pressure drop presents an ever increasing problem in leakage of the engine's cooling air across the rim area of the turbine disk where the blades are mounted thereon. This is particularly the case when the root of the blade is configured in a firtree shape that fits into a complementary shaped broach formed in the rim of the supporting turbine disk. Obviously, the leakage across the rim area is a deficit in terms of engine performance and is a problem that necessitates a solution.
As one skilled in this art appreciates, one of the methods for solving this problem in heretofore known turbine power plants of the type where the pressure drop was not as large as that being considered in today's modern day engines, is by use of a cover plate mounted on the aft end of the turbine disk. This coverplate serves to seal between the disk and the blade and prevents leakage of the engine's cooling air in this area.
Because the rotational speed and temperature of the turbine rotor are so high at this station of the engine, the cover plate is precluded as being viable as a seal for this area. This is because at these higher rotational speeds and temperatures, the cover plate can not be extended out to the blade platform where the leakage occurs. The problem is acerbated because the leak path between the disk lug and the underside of the blade platform opens up as the rotor speed and blade temperature increase. To even add to the leakage problem the "G" loadings are significantly high at this location and together with the high temperature, this area is extremely difficult to seal.
We have found that we can obviate the leakage problem by providing a discreetly contoured seal at a judicious location at the aft end of the rim of the turbine disk inserted into a groove formed in the disk lug and retained by the projection (buttress) under the platform at the aft end of the blade attachment. The seal is free floating in the groove and is sized so that its center contacts the buttress of the blade and the centrifugal force, when the rotor rotates will tend to deform the seal until it contacts the sides of the groove in the disk. This forms an efficacious three (3) point sealing and prevents cooling air from leaking under and around the seal.